(1) Field of the Invention
This invention relates to a method of and a system for inspecting performance (or capacity) of heat-insulation of a pipeline unit having a heat-insulating layer for the purpose of temperature maintenance.
(2) Description of the Prior Art
A pipeline for transporting a cooling medium having temperature lower than ambient temperature, or a higher temperature fluid such as steam, fuel heavy oil or the like is usually provided with a heat-insulating material for the purpose of maintaining cold or hot temperature, such as foamed polyurethane, as the outer layer thereof, and units of these pipelines are prefabricated in a workshop and in a length of, for example, 10 to 15 m as a usual standard length of transportation steel pipes.
In such a case, an insulating material of polyurethane is foamed in a gap having a necessary thickness between a transportation steel pipe and a polyethylene or spiral steel pipe for protecting polyurethane. In order to form a polyurethane foamed layer having no unfilled part in the above-mentioned gap on this occasion, a raw material liquid of polyurethane in an amount slightly greater than the necessary amount is usually poured in the above-mentioned gap. However, even by such an arrangement, it is often experienced on actual working spots that polyurethane non-uniformly foams to create locally unfilled part, resulting in non-uniform insulating effect and trouble in the operation of the fluid transportation pipe. Such non-uniformity of insulating effect is experienced not only at the time of polyurethane foaming but also in the use of other shaped insulating material.
Accordingly, it has been necessary to inspect non-uniformity of the above-mentioned insulating layer but there has been no effective method. For example, there has been adopted such a method as the one in which internal foaming is observed by naked eyes by using, as a cover on the insulating material, a polyurethane sheet which is as thin as possible and nearly transparent, or another in which some samples are taken out from prefabricated unit pipes and cut to inspect the foaming state. However, both the methods have not been perfect. It may also be considered to inspect the whole surface of all the unit pipes by way of X-ray but since operation of X-ray apparatus needs special attention, technique and installation, this idea is not practical particularly for long distance pipelines.